The present invention generally relates to regulating the flow of a gas to a patient.
Inhalation of oxygen, oxygen enriched air and a variety of other gases, vapors and liquid mists (aerosols) is a well-established treatment and well known in the art. Commonly, oxygen administration is carried out in hospital and other medical facility environments. This treatment has been extended to use in the home and other non-medical environments. Generally, at the outset, oxygen administration is carried out under professional medical supervision. In chronic or extended treatment cases, once the therapy has been established, continuous medical supervision is not required and patients use oxygen therapy outside the hospital environment, permitting them to lead active productive lives. Examples of such instances include patients suffering from chronic bronchitis, asthma, emphysema, occupational lung diseases and other lung associated conditions as well as cases involving breathing difficulty due to physical conditions, such as broken ribs and the like.
However, such long term oxygen therapy is generally carried out with a fixed prescribed flow rate, irrespective of a patient""s changing needs during the course of a day. For example, a patient requires less oxygen while lying or asleep than when physically active. During the course of a day, a patient may have a change of circumstances, which would require a variation in oxygen flow rate.
A widely used primary portable supply of oxygen is a high-pressure metal cylinder. Where a patient has such a cylinder of oxygen, exhaustion of that cylinder represents a hazard especially to patients incapable of connecting another, spare cylinder. Recently, alternative oxygen generating devices have been developed. These are portable, light and may be positioned wherever the patient desires. Oxygen generators are electrically operated, draw air from the local environment and reduce the nitrogen content of the air to produce an oxygen rich mixture. There is, however, a significant potential hazard. In the event of a power failure and subsequent oxygen supply failure, it is necessary to have a back-up cylinder of oxygen, which must be manually connected to the patient""s inhaler.
Within the scope of determining the blood oxygen level of a patient, generally, non-invasive blood oxygen measuring devices are preferred to invasive devices. An example of an invasive device is the so-called blood oxygen machine. However, a commonly utilized non-invasive device, called an oximeter, is used for measuring the level of oxygen in the bloodstream. This non-invasive instrument includes a fastening device, a Light Emitting Diode (LED) and a photo-diode. This device emits a signal, which is a function of the oxygen level of the bloodstream. In addition, it sends out a pulse rate signal. Alternative devices include electrochemical, paramagnetic or laser absorption detection and the quenching of luminescence from a metalloporphyrin supply. The desirable physical characteristics of such a sensor include that it be small, robust with respect to environmental perturbations, and have a fast response time.
There is a need in the art, insofar as no provision is generally made, to monitor the patient""s blood oxygen level so as to give an indication of the flow rate of oxygen required to maintain a desired blood oxygen level in the patient. Furthermore, no provision is generally made to effect replacement of a failed or exhausted primary oxygen supply to the patient without having to resort to manually connecting an alternative supply.
Generally, a patient undergoing oxygen therapy is prescribed a flow rate of oxygen by a medical professional. However, in many chronically ill patients, outside of hospitals there is little or no supervision by medically qualified personnel.
The present invention largely eliminates the need for constant supervision and provides a method and apparatus for controlling an appropriate flow of oxygen, sympathetic to a patient""s changing needs. The technique includes measuring the concentration of oxygen in a patient""s bloodstream and comparing this measurement with a desired level of oxygen. Using this comparison, the flow of oxygen to the patient is constantly regulated to optimally maintain the blood oxygen level at the desired level. This is an ongoing process so that any change in the patient""s situation and consequent change in blood oxygen level will be compensated for, by a controlled change in the oxygen flow rate.
The present invention aims to control a flow of oxygen to a patient, responsive to a metric of the oxygen level in the patient""s bloodstream. The present invention makes operating an oxygen inhalation system largely independent of medical supervision and the patient less dependent on assistance. Moreover, the present invention provides a solution to the problem of failure of gas flow from the primary oxygen supply by automatically initiating a replacement flow from an auxiliary emergency supply.
According to a preferred embodiment of the present invention, there is provided a method for controlling a flow of gas from a gas supply to a patient, the method including the following steps:
One) providing a regulated flow of a predetermined gas from a gas supply to a patient so as to increase the concentration in the patient""s bloodstream of a preselected dissolved substance;
Two) measuring the concentration of the preselected dissolved substance in the patient""s bloodstream;
Three) producing an output signal indicative of the measured concentration; and
Four) comparing the measured concentration of the preselected dissolved substance with a desired concentration thereof, so as to determine sufficiency of the regulated flow of the predetermined gas to the patient, and adjusting the regulated flow in accordance therewith.
According to a first preferred embodiment of the present invention, there is, in response to a failure of the flow of the predetermined gas, the additional step of initiating a flow of a predetermined gas from an auxiliary gas supply, thereby to maintain a flow of gas to the patient. This step occurs in response to a failure of the step of providing a regulated flow of a predetermined gas from a gas supply to a patient.
According to a variation of the first embodiment of the present invention, the additional step of initiating a flow of gas includes the sub-step of detecting a failure of the regulated gas flow from the gas supply below a predetermined gas flow.
According to a second embodiment of the present invention, the step of comparing the measured concentration of the preselected dissolved substance with the desired concentration includes the additional step of assigning, prior to the step of measuring the concentration of the preselected dissolved substance in the patient""s bloodstream, at least one of the following:
One) a maximum desired concentration of the preselected dissolved substance in the patient""s bloodstream; and
Two) a minimum desired concentration of the preselected dissolved substance in the patient""s bloodstream.
According to a third embodiment of the present invention, in the step of providing a regulated flow of a predetermined gas from a gas supply to a patient and the step of measuring a concentration of the preselected dissolved substance, the preselected dissolved substance is oxygen.
According to a fourth embodiment of the present invention, the step of measuring the concentration of the preselected dissolved substance in the patient""s blood stream may be either invasive or non-invasive measuring.
According to a fifth embodiment of the present invention, in the step of providing a regulated flow of a predetermined gas, the predetermined gas contains oxygen.
Additionally, according to a sixth embodiment of the present invention, in the step of providing a regulated flow of a predetermined gas, the predetermined gas is substantially oxygen.
In accordance with another preferred embodiment of the present invention, there is provided apparatus for controlling a flow of gas from a gas supply to a patient, which includes:
One) a regulating valve arranged in association with a gas supply, for regulating a flow of gas therefrom to a patient in response to predetermined control signals;
Two) a sensor for measuring a concentration of a preselected dissolved substance in the blood stream of the patient and for providing an output signal indicative of the concentration of the measured substance;
Three) input apparatus for inputting a desired concentration of the dissolved substance in the patient""s bloodstream; and
Four) comparator apparatus associated with the automatic regulating valve, the sensor and the input apparatus, operative to compare a measured concentration with the desired concentration so as to determine sufficiency of the regulated flow of the predetermined gas to the patient, and so as to provide to the regulating valve a control signal so as to adjust the regulating valve in accordance with the determined sufficiency of the regulated flow.
According to a seventh embodiment of the present invention, the gas supply is a primary gas supply, and the apparatus for controlling a flow of gas from a gas supply to a patient also includes:
One) an auxiliary gas supply;
Two) a selector valve for selecting between a gas flow from the primary gas supply and from the auxiliary gas supply; and
Three) detector apparatus for detecting a failure of the flow of gas to the patient from the primary gas supply and for producing a failure signal indicative thereof.
According to a variation of the seventh embodiment of the present invention, the detector apparatus for detecting a failure of the gas flow to the patient from the primary gas supply includes a measuring device for measuring the flow of gas from the primary gas supply. Consequent to a reduction in the flow of gas from the primary gas supply below a predetermined flow, the measuring device produces the failure signal indicative thereof.
According to another variation of the seventh embodiment of the present invention, the selector valve is operable so as to select a gas flow from either the primary gas supply or the auxiliary gas supply. The selector valve operates to select a flow of gas from the auxiliary gas supply in response to the failure signal produced by the detector apparatus.
According to an eighth embodiment of the present invention, the sensor is either an invasive or a non-invasive measuring device.
According to a ninth embodiment of the present invention, the sensor includes apparatus for measuring dissolved oxygen in a blood stream.
In accordance with a further preferred embodiment of the present invention there is provided a program storage device readable by machine, tangibly embodying a program of instructions executable by the machine to perform method steps for controlling a flow of gas from a gas supply to a patient, the method steps include:
One) providing a regulated flow of a predetermined gas from a gas supply to a patient so as to increase the concentration in the patient""s bloodstream of a preselected dissolved substance;
Two) measuring the concentration of the preselected dissolved substance in the patient""s bloodstream;
Three) producing an output signal indicative of the measured concentration; and
Five) comparing the measured concentration of the preselected dissolved substance with a desired concentration thereof, so as to determine sufficiency of the regulated flow of the predetermined gas to the patient, and adjusting the regulated flow in accordance therewith.